Mac Pro - Can I RAID 0+1 from the boot drive???

Stripe (RAID0) with my boot drive and RAID1 to a third drive. Can this been done with the latest Leopard? I am very confused Apple say you can with Leopard, sorry I can't find the link to there page that say's you can. But almost everywhere I look people are saying you can't. I tried doing it last night, and I can't, yet!!! some people have done it, non of which I've seen at least, say how.